1. Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
2. In a medium bowl, whisk together the flour, cocoa powder, baking powder, and salt. Set aside.
3. In a large bowl, combine the melted butter and sugar, stirring until smooth.
4. Add the eggs and vanilla extract to the butter mixture, beating well until fully incorporated.
5. Gradually fold the dry ingredients into the wet mixture, stirring just until combined.
6. Gently fold in the chocolate chips and walnuts, if using.
7. Drop tablespoons of dough onto the prepared baking sheet, leaving enough space for the cookies to spread slightly.
8. Bake for 10-12 minutes, or until the edges are set but the centers remain soft. Remember, they will continue to cook on the baking sheet as they cool.
9. Let the cookies cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.

One of my favorite tips is to slightly underbake the cookies for that truly fudgy center. Mama Lou always stressed the importance of a gentle hand when folding in the dry ingredients to keep the cookies tender and soft.